The present invention relates to a fuel injection system for an internal combustion engine and a vehicle.
Fuel injection systems of internal combustion engines, in particular systems for injection of fuel directly into combustion cylinders of compression ignition engines, may be featuring a control valve for pressure relief from a nozzle of an injector for injecting fuel into a combustion chamber of the internal combustion engine. Such solutions are typically applied in common rail injection systems for preventing a leakage of fuel through a closed nozzle, which is otherwise difficult to avoid when using low viscosity fuels such as DME.
An example of such a system known from prior art is shown in FIG. 1. In that system, designed for operation with DME, there are automatic isolating valves (AIV) employed for preventing leakage of fuel from the fuel supply system through closed nozzles into engine's cylinders when the engine is stopped. These automatic isolating valves are referenced to ambient pressure and are designed to be open when the fuel feed pump is ON and the pressure at the return line of the injectors is higher than DME vapour pressure, and to be closed to prevent access of DME to injectors when the feed pump is OFF. The description of a typical AIV is given, for example, in U.S. Pat. No. 6,189,517 B1. One of the AIVs is placed at the high-pressure port of each of the injectors. The return lines of the injectors are connected together and a common low-pressure AIV is placed downstream of that connection. By this means, the number of low-pressure AIVs is kept to a minimum to make the fuel injection system simpler. It is also known from prior art to position the high-pressure AIV directly upstream of the nozzle, but that design leads to increased control leakage and worse injection controllability at small injected quantities because of the associated volume increase in the high-pressure circuit that is drained between injections. Consequently, the prior art system shown in FIG. 1 offers improved injection controllability at smaller control leakage and is relatively simple due to the total number of AIVs per engine being equal to the number of injectors plus one.
However, in that prior art system, the total volume of fuel confined between the nozzle and the AIVs can be relatively large, depending on the particular design of the injector. It is known, for example, to utilise the entire inter-injector volume as part of the return line in order to simplify design and port interfaces of constituent components. In that case, the total volume of fuel that may escape through the nozzle into engine's combustion chamber when the engine is stopped could be large enough to cause engine startability problems, such as cylinder overpressure at the first ignition. This would also increase total fuel consumption and emission of unburnt hydrocarbons.
The use of automatic isolating valves increases the cost and complexity of a fuel injection system, because, as a reference to a third pressure is necessary for such a valve to operate, appropriate flow path for that extra pressure must be provided as well as extra sealing.
It is desirable to provide a fuel injection system that ensures a better engine startability and reduced fuel leakage whilst the cost and complexity of the system are kept to a minimum.
According to a first aspect of the invention there is provided a fuel injection system for an internal combustion engine, incorporating an engine management system (EMS) 20, a return line 13 connected to a low-pressure fuel system 4, a common rail 6 for storing and supplying a relatively high-pressure fuel to an injector 7, and an automatic isolating valve 8 installed between the common rail 6 and the injector 7. Said injector has a nozzle 11 for injecting fuel into the engine. A valve 10 operated by the EMS 20 is installed between the common rail 6 and the nozzle 11. A spill valve 12 operated by the EMS 20 is connected by its inlet to an outlet of the valve 10 and by its outlet to the return line 13. A check valve 25 is provided between the nozzle 11 and the return line 13, with the inlet of said check valve being connected to the inlet of the nozzle 11.
In other example embodiments said check valve 25 may be connected by its inlet to the outlet of the spill valve 12. The valve 10 may be electrically operated by the EMS 20. The valve 10 may be controlled by an electrically operated pilot valve 9. The outlet of said pilot valve 9 may be connected to the outlet of said spill valve 12. The valve 10 may be controlled by an electrically operated pilot valve 9; the outlet of said pilot valve 9 may be connected to the outlet of said check valve 25.
According to another aspect of the present invention there is provided a fuel injection system for an internal combustion engine, incorporating an engine management system (EMS) 20, a return line 13 connected to a low-pressure fuel system 4, a common rail 6 for storing and supplying a relatively high-pressure fuel to an injector 7, an automatic isolating valve 8 installed between the common rail 6 and the injector 7, and a nozzle 11 for injecting fuel into the engine. A valve 10 is installed between the common rail 6 and the nozzle 11 and controlled by an electrically operated pilot valve 9. An electrically operated spill valve 12 is connected by its inlet to the outlet of the valve 10 and by its outlet to the return line 13. The outlet of said pilot valve 9 is connected to the outlet of said valve 10.
According to yet another aspect of the invention there is provided a vehicle comprising a fuel injection system as disclosed above.